1. The Field of the Invention
The present invention relates to the manufacture of colloids containing metal nanoparticles. More particularly, the invention relates to concentrated metal nanoparticle colloids that are stabilized using a base.
2. Related Technology
Particulate catalysts are an important component of many industrial applications such as refining, organic synthesis, fine chemicals manufacturing, and many other industrial processes. Many of these catalyzed reactions require the use of precious metals such as platinum and palladium. Much effort has been made to make high performance catalysts that improve product yields for a given amount of precious metal used.
One technique for making high performance catalysts is to form particles in a solution using metal salts and an organic dispersing agent. The metal salts are dissolved in a solvent, reacted with the organic agent, and then reduced to cause formation of nanoparticles dispersed in the solvent. Because the particles are very small, e.g., less than 1 micron, the dispersed particles form a colloid. The colloidal particles are typically deposited on a catalyst support.
One problem with making catalysts through a colloidal process is that the concentration of metal must be kept low to prevent precipitation and agglomeration of the metal. Using known manufacturing techniques, attempts to make concentrated colloids have resulted in loss of the precious metal particles. Concentrating the colloid destabilizes the particles and causes the particles to agglomerate and/or precipitate. Particles that precipitate are not suitable for use as high performance catalysts and/or cannot be easily deposited on a support material.
Consequently, existing methods for manufacturing supported nanoparticles catalyst use metal colloids that have dilute concentrations of metal particles. The low concentration metal colloids are somewhat difficult to use because of the relatively large solvent requirements. If the colloid is to be shipped, the excess weight and volume of the solvent significantly increases shipping costs. In addition, applying the particles to a support material is more difficult and expensive because the excess solvent must be removed.